1. Field of the Invention
The present invention relates to a lens driving control apparatus that drives a lens unit in the optical axis direction using a voice coil motor, the lens unit being configured such that a lens is incorporated in a lens barrel.
2. Description of the Related Art
Each of most models of existing portable phones is a so-called “camera-included portable phone” that is mounted with a camera. A camera mounted on a camera-included portable phone is generally configured using a so-called “camera module” formed by integrating a solid state image sensing device such as a CMOS image sensor, a CCD image sensor, etc., with a lens unit that projects an object image onto the solid state image sensing device.
Many of the cameras mounted on the camera-included portable phones each have an automatic focusing function that automatically focuses on an object and, in a camera module with the above automatic focusing function, focusing adjustment can be executed by displacing a lens unit for focusing adjustment in the optical axis direction.
A camera module with an automatic focusing function can be a camera module that is adapted to drive a lens unit that is configured by a lens incorporated in a lens barrel in the optical axis direction using a voice coil motor (see, for example, Japanese Patent Application Laid-Open Publication No. 2006-087282).
The above camera module using a voice coil motor is adapted, for example, to support a lens unit being displaceable against a frame using springs, and to attach a driving coil to the lens unit and drive the lens unit in the optical axis direction using a voice coil motor including a magnetic circuit that forms a magnetic field that acts on the driving coil. The driving of the lens unit is controlled by a lens driving control apparatus that controls a driving current supplied from a motor driver to the driving coil of the voice coil motor.
In the camera module using the voice coil motor as above, when the lens unit is significantly displaced in the optical axis direction to focus on an object image, the lens unit collides with the frame and an impulsive sound is generated.
For a lens driving control apparatus of a conventional camera module, the generation of this impulsive sound has not been especially considered as a problem and no measures have been taken against the impulsive sound.
However, the generation of the impulsive sound is not preferable for the quality level and, with the increase of the driving speed of the lens unit, the impulsive sound can not be ignored.